A preliminary study has indicated that Herpes Simplex Virus Type 2 (HSV-2) will not replicate in an SV40-transformed hamster cell line, even though HSV-1 replicates normally. The presence of specific intranuclear HSV antigens indicates a non-productive infection. An extract of the cells preferentially represses HSV-2 synthesis in an indicator cell line. HSV-1 replication is not affected. The purpose of this study is to characterize the non-productive infection by HSV-2 and to determine the mode of action of the repressor substance upon the regulation of HSV-2 synthesis.